Variations of names for this movement include: Flashing the Arms, Fend Off and Push Away with Arms, Unfolding Arms Like a Fan, Fan Through the Back, Flashing the Arms, Shunting with Both Hands Fanned, 扇通背 : Shan Tong Bei : Fan Through the Back.

The general direction of movement is in a straight line from E3 towards W9 in Movement #20.

From the final posture of “Pick Up the Needle from the Bottom of the Sea” (19c = 20a), begin by lifting the left leg up and then stepping forward onto the left heel (20b-20c). Lift the left hand and move it forward towards E3, fingers upward, palm facing S6 (20b-20c). The right hand moves up and back to the left, finishing above head level, palm facing S6, fingers pointing upward (20c-20d). Sink the body weight into the left leg, and take a left bow stance (20c-20d). Inhale 20a-20c, and exhale 20c-20d.
(20d) (20d) (20d)

The general direction of movement is in a straight line from E3 towards W9 (21a-21h). Exhale on the punch (21g-21h). Please study the recommended online videos to see how the series of postures in this particular movement are performed.
21a = 20d.

Here is a detailed description of how to perform Deflect, Parry and Punch (#21, 21a-21h) taken from the very useful narrative document by David Hann:

“Turn, Intercept, and Punch: Turn to the right on your left heel so that you are facing to your rear, looking over your right shoulder (21b). Your left hand is held, palm facing out, at least a hand’s width from your head. Your right hand is formed into a fist, held about chest level, with the elbow below the fist (21c). Step out with your right foot and strike out and downward with the back of your fist (21d). Step up to your right foot with your left foot, toe down, heel up (21e). Bring your right fist back to your right waist (21f). Bring your left arm across your body as if blocking an opponent’s punch and bring your left hand, palm open, facing and in front of your right fist (21f). Step forward with the left foot (21g) and punch with your right fist (21g-21h), moving it over your left hand, which is now turned flat, palm up (21h).”
– David Hann, Yang Style Short Form Tai Chi
(21e-21f) (21h)*
* Note: In this photo, we see more of the Wu Style of Taijiquan realization of Punch (21h). Notice how far forward the man leans, with his feet rather close in a right bow stance. Notice how the left hand touches the right arm on the inside of the forearm near the elbow. In the 24 Form, the final posture (21h) is much more upright, without leaning forward so much.

The general direction of movement is in a straight line from E3 towards W9 (22a-22g).
From the end of Deflect, Parry and Punch (21h = 22a), begin by drawing the left hand under the right hand from the forearm towards the right hand (22a-22b). Both hands come together in front of the body facing W9 (22c). Draw both arms backwards towards the body (22d-22e) as the weight shifts backwards into the right leg (22d). As both hands reach the waist (22e) the weight is in the back right leg (22e) and the left toe rises (22e). Begin to move forward again in the direction of W9, drawing the weight into the left leg and taking a left bow stance (22f-22g). Both arms Push (An) forward, palms out, elbows bent, pushing in the direction of W9. The waist faces W9 (22g) and the eyes gaze towards an imaginary opponent in front of you (22g). Inhale 22c-22e, and exhale 22f-22g.
(22g) (22g)

23. Cross Hands

Variations of names for this movement include: Crossing Your Hands in Front of Chest, Close the Door, Cross Hands, Cross Your Hands,十字手 : Shi Zi Shou : Cross Hands.
Begin from the Push (An) position (23a = 22g. Gradually turn the front of the body to the right so as to face N12 (23a-23b). Draw the right hand in an arc out and across to the left (23b). Draw the weight into the right leg (23c). Open the arms wide to both sides (23c), palms facing forward, arms about shoulder height. Step the right foot back to shoulder width stance (23d). Draw both arms down in an arc (23d) then up to cross the hands in front of the chest, holding the right hand in front of left hand (23e). Face in the direction of N12 (23e). Inhale at 23b-23c, and exhale at 23e.
(23e)

24. Closing Posture of Taijiquan

Variations of names for this movement include: Conclusion, Concluding Posture, Taiji Ending, Ending Posture, Closing Posture of Taijiquan, 收式 : Shou Shi : Closing.
From the final posture of the “Cross Hands” movement (23e = 24a), begin by moving both arms down and outward (24a) until they reach the waist level (23a-24b). The arms continue downward until they are fully extended downward, hands resting against the sides of the thighs (24c). Step to the right with the left leg (24c) until the left foot is immediate beside the right foot (24d). The final position is identical to posture 1a. Keep in mind all the principles discussed for the posture 1a. You have now finished a full performance of the Tai Chi 24 Form. Inhale at 24a, exhale at 24c. Inhale at 24c, exhale at 24d. The body is facing in the direction of N12, as it was in posture 1a.